Heating element, manufacturing method thereof, composition for forming heating element, and heating apparatus

ABSTRACT

A heating element includes a plurality of matrix particles and a conductive inorganic filler disposed at interfaces between the plurality of matrix particles to provide a conductive network.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of Korean PatentApplication No. 10-2016-0166967, filed on Dec. 8, 2016, and KoreanPatent Application No 10-2017-0147613, filed on Nov. 7, 2017, in theKorean Intellectual Property Office, and all the benefits accruingtherefrom under 35 U.S.C. § 119, the contents of which in their entiretyare incorporated herein by reference.

BACKGROUND 1. Field

The present disclosure relates to a heating element, a method ofmanufacturing the same, a composition for forming the heating element,and a heating apparatus including the heating element.

2. Description of the Related Art

Heat generating elements, which may be used in an electric heatingapparatus, such as an electric oven, generate heat by Joule heatingusing a resistive and conductive composite, and thus have excellentthermal properties. However, these heat generating elements cannotuniformly generate heat due to geometric limitations, and thus have lowheat generation efficiency. Thus, sheet-type heating elements that heata two-dimensional plane have drawn a great deal of attention andinterest.

It is thus desirable to provide a heat generating element capable ofproducing uniform heat.

SUMMARY

Provided is a heating element having high electrical conductivity andexcellent heat generating characteristics.

Provided is a composition for forming the heating element.

Provided is a method of manufacturing the heating element.

Provided is a heating apparatus including the heating element.

According to an aspect of an embodiment, a heating element includes aplurality of matrix particles; and a conductive inorganic fillerdisposed at interfaces between the plurality of matrix particles toprovide a conductive network.

The heating element may include about 5% to about 99.9% by volume of thematrix particles and about 0.01% to about 95% by volume of theconductive inorganic filler, based on a total volume of the matrixparticles and the conductive inorganic filler.

The heating element may include about 95% to about 99.9% by volume ofthe matrix particles and about 0.1% to about 5% by volume of theconductive inorganic filler, based on a total volume of the matrixparticles and the conductive inorganic filler. Since a percolationthreshold of the heating element may decrease, high electricalconductivity may be obtained with a small amount of the conductiveinorganic filler.

An effective conductivity of the heating element is 30% or greater,wherein effective conductivity is an amount of the conductive inorganicfiller contributing actual electrical conductivity compared to the totalamount of the conductive inorganic filler.

The conductive inorganic filler may be in a form of nano-sheets,nano-rods, or any combination thereof.

The conductive inorganic filler may be in a form of nano-sheets having athickness of about 1 nanometer (nm) to about 1,000 nm.

The conductive inorganic filler may include at least one of an oxide, aboride, a carbide, or a chalcogenide.

The oxide may include RuO₂, MnO₂, ReO₂, VO₂, OsO₂, TaO₂, IrO₂, NbO₂,WO₂, GaO₂, MoO₂, InO₂, CrO₂, RhO₂, or any combination thereof, theboride may include Ta₃B₄, Nb₃B₄, TaB, NbB, V₃B₄, VB, or any combinationthereof, the carbide may include Dy₂C, Ho₂C, or any combination thereof,and the chalcogenide may include AuTe₂, PdTe₂, PtTe₂, YTe₃, CuTe₂,NiTe₂, IrTe₂, PrTe₃, NdTe₃, SmTe₃, GdTe₃, TbTe₃, DyTe₃, HoTe₃, ErTe₃,CeTe₃, LaTe₃, TiSe₂, TiTe₂, ZrTe₂, HfTe₂, TaSe₂, TaTe₂, TiS₂, NbS₂,TaS₂, Hf₃Te₂, VSe₂, VTe₂, NbTe₂, LaTe₂, CeTe₂, or any combinationthereof.

The matrix particles may include a glass, an organic polymer, or anycombination thereof.

The glass is formed from a glass frit including at least one of asilicon oxide, a lithium oxide, a nickel oxide, a cobalt oxide, a boronoxide, a potassium oxide, an aluminum oxide, a titanium oxide, amanganese oxide, a copper oxide, a zirconium oxide, a phosphorus oxide,a zinc oxide, a bismuth oxide, a lead oxide, or a sodium oxide.

The glass is formed from a glass frit including at least one of a zincoxide-silicon oxide, a zinc oxide-boron oxide-silicon oxide, a zincoxide-boron oxide-silicon oxide-aluminum oxide, a bismuth oxide-siliconoxide-, a bismuth oxide-boron oxide-silicon oxide, a bismuth oxide-boronoxide-silicon oxide-aluminum oxide, a bismuth oxide-zinc oxide-boronoxide-silicon oxide, or a bismuth oxide-zinc oxide-boron oxide-siliconoxide-aluminum oxide compound.

The organic polymer may include at least one of a polyimide (PI), apolyphenylenesulfide (PPS), a polybutylene terephthalate (PBT), apolyamideimide (PAI), a liquid crystalline polymer (LCP), a polyethyleneterephthalate (PET), polyphenylene sulfide (PPS), or apolyetheretherketone (PEEK).

According to an aspect of another embodiment, a composition for forminga heating element includes functionalized matrix particles, a conductiveinorganic filler, and a solvent.

The matrix particles may include a glass, an organic polymer, or anymixture thereof.

The glass is formed from a glass frit including at least one of asilicon oxide, lithium oxide, nickel oxide, cobalt oxide, boron oxide,potassium oxide, aluminum oxide, titanium oxide, manganese oxide, copperoxide, zirconium oxide, phosphorus oxide, zinc oxide, bismuth oxide,lead oxide, and sodium oxide.

The glass frit is formed from a glass including at least one of a zincoxide-silicon oxide, a zinc oxide-boron oxide-silicon oxide, a zincoxide-boron oxide-silicon oxide-aluminum oxide, a bismuth oxide-siliconoxide, a bismuth oxide-boron oxide-silicon oxide, a bismuth oxide-boronoxide-silicon oxide-aluminum oxide, a bismuth oxide-zinc oxide-boronoxide-silicon oxide, or a bismuth oxide-zinc oxide-boron oxide-siliconoxide-aluminum oxide-compound.

The organic polymer may include at least one of a polyimide (PI), apolyphenylenesulfide (PPS), a polybutylene terephthalate (PBT), apolyamideimide (PAI), a liquid crystalline polymer (LCP), a polyethyleneterephthalate (PET), a polyphenylene sulfide (PPS), or apolyetheretherketone (PEEK).

The matrix particles may be surface-functionalized with positive chargesor negative charges.

The matrix particles may be functionalized with negative charges and mayinclude at least one of a hydroxide ion (OH⁻), a sulfate ion (SO₄ ²⁻), anitrate ion (NO₃ ⁻), an acetate ion (CH₃COO⁻), a permanganate ion (MnO₄⁻), a carbonate ion (CO₃ ²⁻), a sulfide ion (S²⁻), a chloride ion (Cl⁻),a bromide ion (Br⁻), or an oxide ion (O²⁻).

The conductive inorganic filler may be in a form of nano-sheets,nano-rods, or any combination thereof.

The conductive inorganic filler may be in a form of nano-sheets having athickness of about 1 nm to about 1,000 nm.

The conductive inorganic filler may have an electrical conductivity of1,250 Siemens per meter (S/m) or greater.

The conductive inorganic filler may include at least one of an oxide, aboride, a carbide, or a chalcogenide.

The oxide may include RuO₂, MnO₂, ReO₂, VO₂, OsO₂, TaO₂, IrO₂, NbO₂,WO₂, GaO₂, MoO₂, InO₂, CrO₂, RhO₂, or any combination thereof, theboride may include Ta₃B₄, Nb₃B₄, TaB, NbB, V₃B₄, VB, or any combinationthereof, the carbide may include Dy₂C, Ho₂C, or any combination thereof,and the chalcogenide may include AuTe₂, PdTe₂, PtTe₂, YTe₃, CuTe₂,NiTe₂, IrTe₂, PrTe₃, NdTe₃, SmTe₃, GdTe₃, TbTe₃, DyTe₃, HoTe₃, ErTe₃,CeTe₃, LaTe₃, TiSe₂, TiTe₂, ZrTe₂, HfTe₂, TaSe₂, TaTe₂, TiS₂, NbS₂,TaS₂, Hf₃Te₂, VSe₂, VTe₂, NbTe₂, LaTe₂, CeTe₂, or any combinationthereof.

The composition may further include at least one of a dispersionstabilizer, an oxidation stabilizer, a weather stabilizer, an antistaticagent, a dye, a pigment, or a coupling agent.

The dispersion stabilizer may include a low-molecular-weight aminecompound, an amine oligomer, an amine polymer, or any combinationthereof.

The composition may further include a binder including at least one of acellulose polymer, an acrylic polymer, a styrene polymer, a polyvinylresin, a methacrylic ester polymer, a styrene-acrylic acid estercopolymer, a polystyrene, a polyvinyl butyral, a polyvinyl alcohol, apolyethylene oxide, a polypropylene carbonate, a polymethylmethacrylate, a ammonium acrylate, an Arabic gum, a gelatin, an alkydresin, a butyral resin, a saturated ester resin, a natural rubber, asilicone rubber, a fluorosilicone, a fluoroelastomer, a syntheticrubber, or any copolymer thereof.

The composition may include about 5% to about 99.9% by volume of thematrix particles and about 0.01% to about 95% by volume of theconductive inorganic filler, based on a total volume of the matrixparticles and the conductive inorganic filler, and about 5 parts toabout 500 parts by volume of the solvent based on 100 parts by volume ofthe total volume of the functionalized matrix particles and theconductive inorganic filler.

According to an aspect of another embodiment, a heating apparatusincludes the heating element.

According to an aspect of another embodiment, a method of manufacturinga heating element includes coating the composition for forming a heatingelement on a substrate, and heat-treating the coated substrate toprovide the heating element.

The coating may be performed by spray coating.

The heat-treating may be performed at a temperature of about 300° C. toabout 1200° C.

According to an aspect of another embodiment, a method of manufacturinga composition for forming a heating element includes functionalizingsurfaces of matrix particles with positive charges or negative charges,and combining the surface-functionalized matrix particles, a conductiveinorganic filler, and a solvent.

The functionalizing may be performed by functionalizing the surfaces ofthe matrix particles with positively or negatively charged functionalgroups.

Additional aspects will be set forth in part in the description whichfollows and, in part, will be apparent from the description, or may belearned by practice of the presented embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects will become apparent and more readilyappreciated from the following description of the embodiments, taken inconjunction with the accompanying drawings in which:

FIGS. 1A to 1E are scanning electron microscope (SEM) images of aheating element manufactured using surface-functionalized matrixparticles and RuO₂ nano-sheets, according to an embodiment;

FIGS. 1F to 11 are SEM images of a heating element manufactured usingmatrix particles which are not surface-functionalized and RuO₂nano-sheets according to an embodiment;

FIG. 2 is a schematic diagram for describing a method of manufacturing aheating element, according to an embodiment;

FIG. 3 is a cross-sectional view of a sheet-type heating elementincluding a heating element, according to an embodiment;

FIG. 4 is a cross-sectional view of the sheet-type heating element ofFIG. 3 in which an insulating layer is disposed between the substrateand the heating element;

FIG. 5 is a cross-sectional view of an apparatus including a heatingelement, according to an embodiment;

FIG. 6 is a magnified cross-sectional view of a region 80A of theapparatus in FIG. 5;

FIGS. 7A and 7B are cross-sectional views of an apparatus including aheating element, according to another embodiment;

FIG. 8A is a graph of zeta potential (millivolts, mV) versus type ofmaterial versus mobility (square centimeters per volt second, cm²/Vs),illustrating the zeta potential and electric mobility of untreatedenamel frit, the enamel frits surface-treated with positive charges, theenamel frit surfaces treated with negative charges, the untreated enamelfrits, and RuO₂ nano-sheets, in accordance with Experimental Example 1;

FIG. 8B is a graph of surface charge intensity versus zeta potential(mV) illustrating the surface charge distribution of the enamel fritssurface-treated with positive charges, the enamel frits surface-treatedwith negative charges, the untreated enamel frits, and the RuO₂nano-sheets, prepared in accordance with Experimental Example 1;

FIG. 9 is a photograph of the sedimentation test results of a neutraluntreated enamel frit (before surface treatment), the enamel fritssurface-treated with positive charges and negative charges, as preparedin accordance with to Experimental Example 1;

FIG. 10 is a photograph of the sedimentation test results of slurrieseach including RuO₂ nano-sheets and the neutral untreated enamel frit(before surface treatment), the enamel frit surface-treated withpositive charges, or the enamel frit surface-treated with and negativecharges, the enamel frits surface-treated with Experimental Example 1;

FIG. 11 is a graph illustrating electrical conductivity (Siemens permeter, S/m) versus the amount of RuO₂ nano-sheets (volume percent, vol%) in accordance with Experimental Example 2;

FIG. 12 is a graph of conductivity versus test sample versus thickness(micrometers, μm), illustrating thickness and electrical conductivity ofheating elements manufactured by mixing 1 vol % of RuO₂ nano-sheets andeither the surface-treated enamel frit (F-enamel) or thesurface-untreated enamel frit (enamel), according to ExperimentalExample 2;

FIG. 13 illustrates properties of a film formed using a heating elementmanufactured using a surface-treated enamel frit and 1% by volume ofRuO₂ nano-sheets according to Experimental Example 2;

FIGS. 14A to 14D illustrates film morphology of heating elements havingvarious thicknesses, and which are formed of surface-treated enamelfrits and surface-untreated enamel frits and 1% by volume of RuO₂nano-sheets, according to Experimental Example 2;

FIGS. 15A and 15B are photographs showing the coating solutions in thepresence (FIG. 15B) and absence (FIG. 15A) of a dispersion stabilizer,according to Experimental Example 3;

FIGS. 16A to 16E are photographs of films formed of heating elementsincluding 0%, 0.1%, 0.5%, 1%, or 2% of a dispersion stabilizer,respectively, prepared according to Experimental Example 3;

FIG. 17 is a graph of conductivity (S/m) versus amount oftetrabutylammonium hydroxide (TBAOH, %), illustrating electricalconductivity and surface roughness of heating elements with respect tothe amount of the dispersion stabilizer, according to ExperimentalExample 3;

FIGS. 18A and 18B are photographs of coating solutions and properties offilms formed of heating elements in the presence (FIG. 18B) and absence(FIG. 18A) of a binder, according to Experimental Example 4;

FIG. 19 is a graph of the concentration of RuO₂NS nano-sheets (vol %)versus temperature (° C.) illustrating the thermal properties of heatingelements manufactured according to Experimental Example 5; and

FIG. 20 visually illustrates the thermal properties at each of thepoints in the heating elements of FIG. 19.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments, examples of whichare illustrated in the accompanying drawings, wherein like referencenumerals refer to like elements throughout. In this regard, the presentembodiments may have different forms and should not be construed asbeing limited to the descriptions set forth herein. Accordingly, theembodiments are merely described below, by referring to the figures, toexplain aspects. As used herein, the term “and/or” includes any and allcombinations of one or more of the associated listed items. “Or” means“and/or.” Expressions such as “at least one of,” when preceding a listof elements, modifies the entire list of elements and does not modifythe individual elements of the list.

It will be understood that when an element is referred to as being “on”another element, it can be directly on the other element or interveningelements may be present therebetween. In contrast, when an element isreferred to as being “directly on” another element, there are nointervening elements present.

It will be understood that when an element is referred to as being “on”another element, it can be directly on the other element or interveningelements may be present therebetween. In contrast, when an element isreferred to as being “directly on” another element, there are nointervening elements present.

It will be understood that, although the terms “first,” “second,”“third,” etc. may be used herein to describe various elements,components, regions, layers and/or sections, these elements, components,regions, layers and/or sections should not be limited by these terms.These terms are only used to distinguish one element, component, region,layer or section from another element, component, region, layer, orsection. Thus, “a first element,” “component,” “region,” “layer,” or“section” discussed below could be termed a second element, component,region, layer or section without departing from the teachings herein.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting. As used herein, thesingular forms “a,” “an,” and “the” are intended to include the pluralforms, including “at least one,” unless the content clearly indicatesotherwise. “At least one” is not to be construed as limiting “a” or“an.” It will be further understood that the terms “comprises” and/or“comprising,” or “includes” and/or “including” when used in thisspecification, specify the presence of stated features, regions,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,regions, integers, steps, operations, elements, components, and/orgroups thereof.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper,” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the exemplary term “below” can encompass both anorientation of above and below. The device may be otherwise oriented(rotated 90 degrees or at other orientations) and the spatially relativedescriptors used herein interpreted accordingly.

“About” or “approximately” as used herein is inclusive of the statedvalue and means within an acceptable range of deviation for theparticular value as determined by one of ordinary skill in the art,considering the measurement in question and the error associated withmeasurement of the particular quantity (i.e., the limitations of themeasurement system). For example, “about” can mean within one or morestandard deviations, or within ±30%, 20%, 10%, or 5% of the statedvalue.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and thepresent disclosure, and will not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

Exemplary embodiments are described herein with reference to crosssection illustrations that are schematic illustrations of idealizedembodiments. As such, variations from the shapes of the illustrations asa result, for example, of manufacturing techniques and/or tolerances,are to be expected. Thus, embodiments described herein should not beconstrued as limited to the particular shapes of regions as illustratedherein but are to include deviations in shapes that result, for example,from manufacturing. For example, a region illustrated or described asflat may have rough and/or nonlinear features. Moreover, sharp anglesthat are illustrated may be rounded. Thus, the regions illustrated inthe figures are schematic in nature and their shapes are not intended toillustrate the precise shape of a region and are not intended to limitthe scope of the present claims.

Conductive materials such as RuO₂, graphene, and carbon nanotubes havebeen researched as substances used to form sheet-type heating elements.The sheet-type heating elements may be manufactured using varioussolution coating methods. The conductive materials and/or matrixmaterials are uniformly distributed in a heating element coatingsolution formed of an inorganic material, in order to improve heatgenerating performance and achieve uniform heat generatingcharacteristics.

As used herein, “composite” refers to a material formed by combining twoor more materials having different physical and/or chemical properties,wherein the composite has properties different from each materialconstituting the composite individually, and wherein particles or wiresof each material are at least microscopically separated anddistinguishable from each other in a finished structure of thecomposite.

When a sheet-type heating element, i.e., a heating element in the formof a sheet, is manufactured, a matrix such as a glass frit and a fillerthat generates heat are mixed together to form a composite. In thiscase, the individual filler particles are connected to each other andwhen the filler particles are electrified (i.e., an electrical currentis applied thereto), heat may be generated. When a heating elementincludes a ceramic material as the filler, the filler particles may havea shape in the form of a sphere or a three dimensional polyhedronstructure. For example, RuO₂ particles having a sphere or polyhedronshape may be used as a filler. When these types of RuO₂ particles areused, theoretical percolation between RuO₂ particles may be possiblewhen the entire surface of the glass frit particles are covered by theRuO₂ particles, and thus stable heat generation may be accomplished.

However, when the RuO₂ particles having a sphere or polyhedron shape areused as a filler, a contact area between the RuO₂ particles is small,and thus a high temperature may be needed for effective sintering andthe amount of RuO₂ particles to be percolated in the matrix may need tobe increased to achieve the desired heat generation.

The heating element according to an embodiment includes a conductiveinorganic filler in the form of nano-sheets, nano-rods, or anycombination thereof. The conductive inorganic filler in the form oftwo-dimensional nano-sheets, one-dimensional nano-rods, or anycombination thereof may form a conductive network at interfaces betweenmatrix particles even when using only a small amount. Furthermore,adjacent nano-sheets may be in surface contact with each other, therebyimproving sinterability. Thus, by using the heating element according toan embodiment, a percolation network is easily established and asintering temperature may be reduced as compared to when a filler havinga sphere or polyhedron shape is used, and higher electric conductivitymay also be obtained even when the same amounts of the filler is used.

Hereinafter, a heating element, a heating apparatus including the same,a composition for forming the heating element, and a method ofmanufacturing the heating element will be described in detail withreference to the accompanying drawings. In the drawings, thicknesses oflayers and regions may be exaggerated for clarity.

A heating element according to an exemplary embodiment includes aplurality of matrix particles and a conductive inorganic filler disposedat interfaces between the plurality of matrix particles to provide aconductive network.

The conductive inorganic filler may exhibit electrical conductivity byforming a conductive network at the interfaces between the matrixparticles. When matrix particles whose surfaces are functionalized withpositive charges or negative charges are used in the preparation of theheating element, the conductive inorganic filler forms a largerconductive network, so that the heating element may have higherelectrical conductivity. Thus, a percolation threshold of the heatingelement may decrease. That is, excellent heat generating characteristicsmay be obtained even when a small amount of the conductive inorganicfiller providing electrical conductivity is used.

When the amount of a conductive nano filler, which contributes to actualelectrical conductivity, compared to the total amount of the conductiveinorganic filler included in the heating element is defined as“effective conductivity”, the heating element may have a high effectiveconductivity. For example, the heating element may have an effectiveconductivity of 30% or greater, i.e., 30% or more of the total amount ofconductive filler contributes to the actual electrical conductivity. Aheating element having an effective conductivity of 30% or greater mayrealize high electrical conductivity even when a small amount of theconductive inorganic filler is used between the matrix particles. Theeffective conductivity of conventional heating elements is less than30%.

The matrix particles may be a glass formed of a glass frit, or anorganic polymer, or any combination thereof.

According to an embodiment, the matrix particles may be formed from theglass frit. The glass frit may include, for example, a silicon oxide, alithium oxide, a nickel oxide, a cobalt oxide, a boron oxide, apotassium oxide, an aluminum oxide, a titanium oxide, a manganese oxide,a copper oxide, a zirconium oxide, a phosphorus oxide, a zinc oxide, abismuth oxide, a lead oxide, or a sodium oxide. Any one or more of theforegoing oxides or their hydrates may be present in the glass of thematrix particles.

For example, the glass frit may include at least one of the followingcompounds. As is known in the art, the compounds may include othercomponents. The compounds include at least one of a zinc oxide-siliconoxide (ZnO—SiO₂), a zinc oxide-boron oxide-silicon oxide(ZnO—B₂O₃—SiO₂), a zinc oxide-boron oxide-silicon oxide-aluminum oxide(ZnO—B₂O₃—SiO₂—Al₂O₃), a bismuth oxide-silicon oxide (Bi₂O₃—SiO₂), abismuth oxide-boron oxide-silicon oxide (Bi₂O₃—B₂O₃—SiO₂), a bismuthoxide-boron oxide-silicon oxide-aluminum oxide (Bi₂O₃—B₂O₃—SiO₂—Al₂O₃),a bismuth oxide-zinc oxide-boron oxide-silicon oxide(Bi₂O₃—ZnO—B₂O₃—SiO₂), or a bismuth oxide-zinc oxide-boron oxide-siliconoxide-aluminum oxide (Bi₂O₃—ZnO—B₂O₃—SiO₂—Al₂O₃) compounds. Any one ormore of the foregoing compounds, or their hydrates or other oxides maybe present in the glass of the matrix particles.

The glass frit may be prepared by adding an additive to silicon oxide,for example. The additive may include at least one of lithium (Li),nickel (Ni), cobalt (Co), boron (B), potassium (K), aluminum (Al),titanium (Ti), manganese (Mn), copper (Cu), zirconium (Zr), phosphorus(P), zinc (Zn), bismuth (Bi), lead (Pb), or sodium (Na). However, theadditive is not limited to the elements described above.

According to another exemplary embodiment, the matrix particles mayinclude an organic material having heat resistance, for example, anorganic polymer. For example, the organic polymer may have a meltingtemperature (Tm) of 200° C. or higher. The organic polymer may be atleast one of a polyimide (PI), a polyphenylene sulfide (PPS), apolybutylene terephthalate (PBT), a polyamideimide (PAI), a liquidcrystalline polymer (LCP), a polyethylene terephthalate (PET), apolyphenylene sulfide (PPS), or a polyetheretherketone (PEEK).

An amount of the matrix particles included in the heating element may befrom about 5 to about 99.99% by volume, for example from about 70 toabout 99.9% by volume, particularly for example, from about 90 to about99.9% by volume, or from about 95 to about 99.9% by volume based on atotal volume of the matrix particles and the conductive inorganicfiller. When the amount of the matrix particles is within these ranges,the matrix particles may sufficiently perform a role as a support forthe conductive inorganic filler to form the conductive network.

In the heating element, the conductive inorganic filler forming theconductive network is disposed at the interfaces between the matrixparticles.

The conductive inorganic filler may be a particulate filler in the formof a plurality of nano materials. For example, the conductive inorganicfiller may be fillers in the form of nano-sheets, nano-rods, or anycombination thereof. The nano-sheet type filler and the nano-rod typefiller may include nano-sheets or nano-rods of various materials.Although the nano-sheets or the nano-rods may have compositionsproviding a predetermined electrical conductivity (e.g., 1250 S/m),electrical conductivity of the nano-sheets and the nano-rods may beslightly less or greater than the predetermined electrical conductivity.

The conductive inorganic filler particles may have a thickness of about1 nm to about 1,000 nm, or about 10 nm to about 900 nm, or about 50 nmto about 750 nm. The conductive inorganic filler particles may have alength of about 0.1 μm to about 500 μm, or about 1 μm to about 400 μm,or about 10 to about 300 μm. When the thickness and the length of theconductive inorganic filler particles are within these ranges above, theconductive network may be formed at the interfaces between matrixparticles.

The nano-sheet type filler or the nano-rod type filler may include atleast one of an oxide, a boride, a carbide, or a chalcogenide.

An oxide used as the conductive inorganic filler may be, for example,RuO₂, MnO₂, ReO₂, VO₂, OsO₂, TaO₂, IrO₂, NbO₂, WO₂, GaO₂, MoO₂, InO₂,CrO₂, RhO₂, or any combination thereof.

A boride used as the conductive inorganic filler may be, for example,Ta₃B₄, Nb₃B₄, TaB, NbB, V₃B₄, VB, or any combination thereof.

A carbide used as the conductive inorganic filler may be, for example,Dy₂C, Ho₂C, or any combination thereof.

A chalcogenide used as the conductive inorganic filler may be, forexample, AuTe₂, PdTe₂, PtTe₂, YTe₃, CuTe₂, NiTe₂, IrTe₂, PrTe₃, NdTe₃,SmTe₃, GdTe₃, TbTe₃, DyTe₃, HoTe₃, ErTe₃, CeTe₃, LaTe₃, TiSe₂, TiTe₂,ZrTe₂, HfTe₂, TaSe₂, TaTe₂, TiS₂, NbS₂, TaS₂, Hf₃Te₂, VSe₂, VTe₂, NbTe₂,LaTe₂, CeTe₂, or any combination thereof.

An RuO_((2+x)) nano-sheet, where 0≤x<0.1, as an example of theconductive inorganic filler in the form of an oxide may be prepared bythe following method. Other oxide-based inorganic fillers may also beprepared using a method which is substantially the same as or similar tothe method used to form the RuO_((2+x)) nano-sheet, where 0<x<0.1.

In order to prepare the RuO_((2+x)) nano-sheet, K₂CO₃ and RuO₂ are mixedin a molar ratio of 5:8, and the mixture is formed as pellets. Thepellets are placed in an alumina crucible and heat treated for 12 hoursin a tube furnace at a temperature of 850° C. The heat treatment may beperformed under a nitrogen atmosphere. The weight of the pellet may bein a range from about 1 g to about 20 g. However, the weight of thepellet may vary. The pellet may have a disc shape.

After heat treatment of the pellet, when the temperature of the tubefurnace is cooled down to room temperature, the alumina crucible isremoved from the tube furnace and the pellet is ground to a powder.

Next, after washing the powder with about 100 milliliters (mL) to about4 liters (L) of water for 24 hours, the powder is collected byfiltering. At this point, the powder has a composition ofK_(0.2)RuO_(2.1).nH₂O.

Next, the K_(0.2)RuO_(2.1).nH₂O powder is immersed in 1 molar (M) HCland stirred for 3 days at room temperature. Afterwards, the powder isrecovered by filtering the mixture. The composition of the powderobtained in this process is H_(0.2)RuO_(2.1).

Next, 1 gram (g) of H_(0.2)RuO_(2.1) powder is immersed in 250 mL of anaqueous solution in which an intercalant, such as tetramethylammoniumhydroxide (TMAOH) and tetrabutylammonium hydroxide (TBAOH) are mixed,and the mixture is stirred for more than 10 days at room temperature. Inthis case, the concentration of TMAOH and TBAOH may be approximatelyTMA+/H+, TBA+/H+=0.1 to about 50. After the stirring process iscompleted, the mixture is subjected to a centrifugation process. Thecentrifugation may be performed for 30 minutes at 2,000 revolutions perminute (rpm). Through the centrifugation process, an aqueous solutionincluding exfoliated RuO_((2+x)) nano-sheets and a precipitate includingun-exfoliated powder are separated from each another.

The concentration of the exfoliated RuO₂ nano-sheets in the aqueoussolution obtained through the centrifugation process is measured usingan ultraviolet-visible spectrophotometer (UVS).

Next, optical absorbency of the RuO₂ nano-sheet aqueous solution withrespect to a wavelength of 350 nm is measured, and the concentration ofthe RuO₂ nano-sheets in the RuO₂ nano-sheet aqueous solution iscalculated using an absorbency coefficient (7400 liters per molecentimeter (L/mol·cm)) of the RuO₂ nano-sheet.

Next, a volume of the RuO₂ nano-sheet aqueous solution is measured whichcorresponds to a desired weight of RuO₂ nano-sheets, and a solvent isremoved from the measured RuO₂ nano-sheet aqueous solution using acentrifugal separator. In this case, the centrifugal separator may beoperated at a speed of 10,000 rpm or greater for 15 minutes or more.

Meanwhile, a chalcogenide nano-sheet may be prepared by the followingmethod.

Raw materials in a solid powder state are prepared. At this point, theraw materials are prepared by weighing appropriate amounts to obtain adesired atomic ratio. Next, the prepared raw materials are uniformlymixed, and afterwards, are made into pellets. After placing the pelletsin a quartz tube, the quartz tube is filled with an argon gas and issealed. The quartz tube in which the pellets are placed is heat treatedin a furnace at a temperature in a range from about 500° C. to about300° C. for about 12 hours to about 72 hours. After the heat treatment,the resultant product is cooled to room temperature, and afterwards, thepellets are removed from the quartz tube and ground into a powder,thereby gaining the pellets in a powder state. Lithium ions are injectedbetween the chalcogenide layers which are in a powder state using alithium ion source. For example, lithium ions may be injected betweenthe chalcogenide layers in the powder state using a lithium ion source,such as n-butyllithium.

As another example, lithium ions may directly be injected between thechalcogenide layers in the powder state using an electrochemical methodinstead of using the lithium ion source.

When lithium ions are injected between the chalcogenide layers in thepowder state, spaces between the individual chalcogenide layers widen,so that the chalcogenide layers, i.e., chalcogenide nano-sheets, may beeasily exfoliated. When the lithium ions are replaced by moleculeshaving a larger size (e.g., water molecules or organic molecules), thespaces between the chalcogenide layers are widened even further. Thus,the chalcogenide nano-sheets may be more easily exfoliated.

As another method of easily exfoliating chalcogenide nano-sheets, afterinjecting lithium ions between the chalcogenide layers formed in apowder state, the chalcogenide layers may be ultrasonicated.

Boride nano-sheets may be prepared by the following two methods.

A first method is the same method as used to prepare the chalcogenidenano-sheets.

A second method is as follows.

Raw materials in a solid powder state are provided. The raw materialsare prepared by weighing appropriate amounts to obtain a desired atomicratio. Next, the prepared raw materials are uniformly mixed and formedinto pellets. After placing the pellets in an arc melting equipment, thepellets are melted at a high temperature using an electric arc. Themelting process using an electric arc may be repeated several (e.g., twoor more) times until the pellets are uniformly mixed to become a singlephase. After the resultant product is cooled down to room temperature,the resultant product is removed from the arc melting equipment and isground, thereby gaining the pellets in a powder state. Afterwards,lithium ions are injected between individual boride layers which are ina powder state. The lithium ions may be injected between the boridelayers formed in a powder state using a lithium ion source, for example,n-butyllithium. Alternatively, lithium ions may directly be injectedbetween the boride layers in the powder state using an electrochemicalmethod instead of using the lithium ion source. When lithium ions areinjected between the boride layers which are in a powder state, spacesbetween the boride layers which are in a powder state may be widened, sothat the boride layers, i.e., boride nano-sheets, may be easilyexfoliated. When the lithium ions are replaced by molecules having alarger size (e.g., water molecules or organic molecules), the spacesbetween the boride layers may be widened even further. Thus, the boridenano-sheets may be more easily exfoliated.

The boride nano-sheets may be exfoliated by injecting lithium ionsbetween the boride layers in a powder state and ultrasonicating theboride layers.

Carbide nano-sheets may be prepared using the same method used toprepare the boride nano-sheets described above.

The conductive inorganic filler in the form of nano-rods may be obtainedusing any method known to those of skill the art.

An amount of the conductive inorganic filler included in the heatingelement may be from about 0.01 to about 95% by volume, for example fromabout 0.1 to about 30% by volume, particularly for example from about0.1 to about 10% by volume, from about 0.1 to about 5% by volume, orfrom about 1 to about 4% by volume, based on the total volume of thematrix particles and the conductive inorganic filler. When the amount ofthe conductive inorganic filler is within these ranges, the conductiveinorganic filler may establish the conductive network at interfacesbetween the matrix particles. Since a percolation threshold is decreasedin the heating element, high electrical conductivity may be obtainedeven when a small amount (e.g., 5% by volume or less) of the conductiveinorganic filler is used.

The amount of the conductive inorganic filler may vary according toelectrical conductivity of the conductive inorganic filler. For example,when the inorganic filler described herein having a high electricalconductivity is used, a heating element having a high electricalconductivity may be obtained even when a small amount of the conductiveinorganic filler is used. For example, when a conductive inorganicfiller having a high electrical conductivity, such as RuO₂, is used, aheating element having excellent electrical conductivity may be preparedwith 10% by volume or less of the conductive inorganic filler, based onthe total volume of the matrix particles and the conductive inorganicfiller.

The conductive inorganic filler may be electrically connected viasurface contact and/or line contact in at least one region of theconductive inorganic fillers, at the interfaces between the plurality ofmatrix particles, thereby forming a conductive network. By using theconductive inorganic filler forming the conductive network, the heatingelement has electrical conductivity. Without being limited by theory, itis believed that since the conductive inorganic filler does notaggregate, but instead establishes surface contact and/or line contactbetween adjacent inorganic fillers, electrical conductivity may beincreased as compared to prior art particulate fillers. Thus, theheating element including the conductive inorganic filler disposed atinterfaces between the plurality of matrix particles according to anembodiment may have higher electrical conductivity than a heatingelement including a particular filler (e.g., a ceramic filler) having ashape in the form of a sphere or a three dimensional polyhedronstructure, even when the same amounts of each filler are used.

The conductive inorganic filler may form a larger conductive network bymanufacturing the heating element using matrix particles whose surfacesare functionalized with positive charges or negative charges, ascompared with the case where the heating element is prepared by usingmatrix particles whose surfaces are not functionalized (i.e.,surface-unfunctionalized) with positive charges or negative charges.Accordingly, the heating element according to an embodiment may haveexcellent electrical conductivity due to the larger conductive networkeven when a small amount of conductive inorganic filler is used. Forexample, as illustrated in FIGS. 11 and 12, in the case where 1% byvolume of the conductive inorganic filler is used based on the totalvolume of the matrix particles and the conductive inorganic filler, aheating element manufactured using matrix particlessurface-functionalized with positive charges or negative charges has anelectrical conductivity of about 150 S/m, whereas a heating elementmanufacturing by using surface-unfunctionalized matrix particles doesnot have electrical conductivity.

The heating element may further include other components in addition tothe matrix particles and the conductive inorganic filler.

Hereinafter, a heating element forming composition for forming a heatingelement according to an embodiment, will be described.

The heating element forming composition includes a plurality offunctionalized matrix particles, a conductive inorganic filler, and asolvent.

The matrix particles may be formed of a glass, an organic polymer, orany mixture thereof.

According to an embodiment, the matrix particles may include glassformed from a frit (e.g., glass frit). The glass frit may include, forexample, at least one of a silicon oxide, a lithium oxide, a nickeloxide, a cobalt oxide, a boron oxide, a potassium oxide, an aluminumoxide, a titanium oxide, a manganese oxide, a copper oxide, a zirconiumoxide, a phosphorus oxide, a zinc oxide, a bismuth oxide, a lead oxide,or a sodium oxide.

For example, the glass frit may include at least one of a zincoxide-silicon oxide (ZnO—SiO₂), a zinc oxide-boron oxide-silicon oxide(ZnO—B₂O₃—SiO₂), a zinc oxide-boron oxide-silicon oxide-aluminum oxide(ZnO—B₂O₃—SiO₂—Al₂O₃), a bismuth oxide-silicon oxide (Bi₂O₃—SiO₂), abismuth oxide-boron oxide-silicon oxide (Bi₂O₃—B₂O₃—SiO₂), a bismuthoxide-boron oxide-silicon oxide-aluminum oxide (Bi₂O₃—B₂O₃—SiO₂—Al₂O₃),a bismuth oxide-zinc oxide-boron oxide-silicon oxide(Bi₂O₃—ZnO—B₂O₃—SiO₂), or a bismuth oxide-zinc oxide-boron oxide-siliconoxide-aluminum oxide (Bi₂O₃—ZnO—B₂O₃—SiO₂—Al₂O₃) compounds. Any one ormore of the foregoing compounds, or their hydrates or other oxides maybe present in the glass of the matrix particles.

The glass frit may be prepared by adding an additive to silicon oxide,for example. The additive may include at least one of lithium (Li),nickel (Ni), cobalt (Co), boron (B), potassium (K), aluminum (Al),titanium (Ti), manganese (Mn), copper (Cu), zirconium (Zr), phosphorus(P), zinc (Zn), bismuth (Bi), lead (Pb), and sodium (Na). However, theadditive is not limited to the elements described above.

According to an embodiment, the matrix particles may include an organicpolymer. The organic polymer may be at least one of a polyimide (PI), apolyphenylene sulfide (PPS), a polybutylene terephthalate (PBT), apolyamideimide (PAI), a liquid crystalline polymer (LCP), a polyethyleneterephthalate (PET), a polyphenylene sulfide (PPS), or apolyetheretherketone (PEEK).

The plurality of matrix particles may be surface-functionalized withpositive charges or negative charges. The matrix particlessurface-functionalized with positive charges or negative charges mayhave improved dispersibility and stability in the heating elementforming composition due to the surface functionalization. In addition,by matching surface charges between the matrix particles and theconductive inorganic filler, dispersion stability of the heating elementforming composition may be improved and thus electrical conductivity ofa film including the heating element may be increased.

The surfaces of the matrix particles may be functionalized with negativecharges. The matrix particles surface-functionalized with negativecharges may include, for example, a hydroxide ion (OH⁻), a sulfate ion(SO₄ ²⁻), a sulfite ion (SO₂ ²⁻), a nitrate ion (NO₃ ⁻), an acetate ion(CH₃COO⁻), a permanganate ion (MnO₄ ⁻), a carbonate ion (CO₃ ²⁻), asulfide ion (S²⁻), a chloride ion (Cl⁻), a bromide ion (Br⁻), a fluorideion (F⁻), an oxide ion (O²⁻), a carboxylate ion (COO⁻), a cyanate ion(OCN⁻), or a tosylate ion (p-toluene sulfonic acid (CH₃C₆H₄SO₃ ⁻)) onthe surfaces thereof, without being limited thereto. In particular, thematrix particles surface-functionalized with negative charges mayinclude, for example, a carboxylate ion (including a higher fatty acidalkali ion, an N-acryl amino acid ion, alkyl ether carboxylic acid ion,or a combination thereof), a sulfonyl ion (including a C1-C20 alkylsulfonic acid ion, a C1-C20 alkyl benzene, a C1-C20 alkyl amino acidion, a C1-C20 alkyl naphthalene sulfonic acid ion, or a combinationthereof), a sulfuric acid ester ion (including a C1-C20 alkyl sulfateion, a C1-C20 alkyl ether sulfate ion, a C1-C20 alkyl aryl ether sulfateion, or a C1-C20 alkyl amide sulfate ion, or a combination thereof), aphosphate ester ion (including a C1-C20 alkyl phosphate ion, alkyl etherphosphate ion, a C1-C20 alkyl aryl ether phosphate ion, or a combinationthereof), and the like.

The matrix particles may be surface-functionalized with positivecharges. The matrix particles surface-functionalized with positivecharges may include cations, for example, an amine ion (NH⁴⁺) on thesurfaces thereof.

In particular, the cations may include simple aliphatic amine ionshaving primary to tertiary amines, quaternary ammonium ions, andso-called onium ions such as phosphonium ions and sulfonium ions, forexample, amine, alkyl, aromatic, and heterocyclic ammonium ions.

The surface functionalization may be achieved by treating the matrixparticles with an ion-containing precursor solution capable ofsurface-functionalizing the matrix particles with positive charges ornegative charges. For example, when the matrix particles are treatedwith a strong acid such as an RCA solution and then dispersed in water,matrix particles having surfaces functionalized with hydroxide ions maybe obtained. The RCA solution is a mixed solution of water(H₂O)/hydrogen peroxide (H₂O₂)/ammonia water (NH₄OH). By using anoxidant such as the RCA solution, the surfaces of the matrix particlesof the heating element may be functionalized with a hydrophilicfunctional group (OH⁻). The matrix particles surface-functionalized witha hydrophilic group such as OH⁻ may be uniformly dispersed in a coatingslurry and do not aggregate with the conductive inorganic fillerstabilized by organic ligands, since the organic ligands are easilyadsorbed to the surfaces of the matrix particles. Thus, a stabledispersion coating solution may be prepared. When coated with such astable coating solution, the conductive inorganic filler may bedispersed and distributed along the matrix (e.g., at interfaces betweenthe matrix particles), thereby forming a stable conductive path.

Such surface-functionalization may also be achieved by treating thematrix particles with an ammonium silane monomer and/or oligomer. Thus,matrix particles whose surfaces are functionalized with positive chargesmay be obtained.

Whether the surfaces of the matrix particles are functionalized withpositive charges or negative charges may be determined by the surfacecharge characteristics of the conductive inorganic filler. For example,when mixed with the conductive inorganic filler having negative charges,for example, RuO₂, the matrix particles may have improved dispersionstability in a solvent via surface functionalization with negativecharges.

The conductive inorganic filler included in the heating element formingcomposition to improve electrical conductivity and/or strength of theheating element, may be in the form of nano-sheets, nano-rods, or anycombination thereof as described above.

The conductive inorganic filler may have a thickness of about 1 nm toabout 1,000 nm, or about 10 nm to about 900 nm, or about 50 nm to about750 nm. The conductive inorganic filler may have a length of about 0.1μm to about 500 μm, or about 1 μm to about 400 μm, or about 10 to about300 μm. When the thickness and the length of the conductive inorganicfiller are within the ranges described above, the conductive network maybe formed at the interfaces between the matrix particles even when onlya small amount of the conductive inorganic filler is present.

The conductive inorganic filler may have an electrical conductivity of250 S/m or higher, for example, about 1,000 S/m or higher, or about1×10⁴ S/m or higher, or about 1×10⁵ S/m or higher, or about 1×10⁶ S/m orhigher.

The conductive inorganic filler may include at least one of an oxide, aboride, a carbide, or a chalcogenide.

The oxide may include RuO₂, MnO₂, ReO₂, VO₂, OsO₂, TaO₂, IrO₂, NbO₂,WO₂, GaO₂, MoO₂, InO₂, CrO₂, RhO₂, or any combination thereof.

The boride may include Ta₃B₄, Nb₃B₄, TaB, NbB, V₃B₄, VB, or anycombination thereof.

The carbide may include Dy₂C, Ho₂C, or any combination thereof.

The chalcogenide may include AuTe₂, PdTe₂, PtTe₂, YTe₃, CuTe₂, NiTe₂,IrTe₂, PrTe₃, NdTe₃, SmTe₃, GdTe₃, TbTe₃, DyTe₃, HoTe₃, ErTe₃, CeTe₃,LaTe₃, TiSe₂, TiTe₂, ZrTe₂, HfTe₂, TaSe₂, TaTe₂, TiS₂, NbS₂, TaS₂,Hf₃Te₂, VSe₂, VTe₂, NbTe₂, LaTe₂, CeTe₂, or any combination thereof.

Electrical conductivities of some of the aforementioned conductiveinorganic fillers are shown in Tables 1 to 3 below. Table 1 shows oxidefiller materials. Table 2 shows boride and carbide filler materials.Table 3 shows chalcogenide filler materials.

TABLE 1 Composition S/m RuO₂ 3.55 × 10⁶ MnO₂ 1.95 × 10⁶ ReO₂ 1.00 × 10⁷VO₂ 3.07 × 10⁶ OsO₂ 6.70 × 10⁶ TaO₂ 4.85 × 10⁶ IrO₂ 3.85 × 10⁶ NbO₂ 3.82× 10⁶ WO₂ 5.32 × 10⁶ GaO₂ 2.11 × 10⁶ MoO₂ 4.42 × 10⁶ InO₂ 2.24 × 10⁶CrO₂ 1.51 × 10⁶ RhO₂ 3.10 × 10⁶

TABLE 2 Composition σ (S/m) Boride Ta₃B₄ 2335000 Nb₃B₄ 3402000 TaB1528800 NbB 5425100 V₃B₄ 2495900 VB 3183200 Carbide Dy₂C 180000 Ho₂C72000

TABLE 3 Composition σ (S/m) AuTe₂ 433000 PdTe₂ 3436700 PtTe₂ 2098000YTe₃ 985100 CuTe₂ 523300 NiTe₂ 2353500 IrTe₂ 1386200 PrTe₃ 669000 NdTe₃680400 SmTe₃ 917900 GdTe₃ 731700 TbTe₃ 350000 DyTe₃ 844700 HoTe₃ 842000ErTe₃ 980100 CeTe₃ 729800 TiSe₂ 114200 TiTe₂ 1055600 ZrTe₂ 350500 HfTe₂268500 TaSe₂ 299900 TaTe₂ 444700 TiS₂ 72300 NbS₂ 159100 TaS₂ 81000Hf3Te₂ 962400 VSe₂ 364100 VTe₂ 238000 NbTe₂ 600200 LaTe₂ 116000 LaTe₃354600 CeTe₂ 55200

As an example of the conductive inorganic filler, RuO_((2+x))nano-sheets (0≤x<0.1) may be used.

The heating element forming composition may include a solvent todisperse the surface-functionalized matrix particles and the conductiveinorganic filler. The solvent may be water or a mixture of water and anorganic solvent miscible with water at room temperature (water-miscibleorganic solvent). For example, at least 90% by weight of the solvent maybe water and more particularly at least 95% by weight of the solvent maybe water. According to an embodiment, about 100% by weight of thesolvent may be water.

Examples of the organic solvent miscible with water at room temperaturemay include a C2-C6 monoalcohol (e.g.: ethanol and isopropanol); aC2-C20 polyol, particularly, a C2-C10 polyol, and more particularly, aC2-C6 polyol (e.g., glycerol, propylene glycol, butylene glycol,pentylene glycol, hexylene glycol, dipropylene glycol, and diethyleneglycol); a glycol ether and particularly a C3-C16 glycol ether (e.g., aC1-C4 alkyl ether of mono-, di-, or tripropylene glycol and a C1-C4alkyl ether of mono-, di-, or triethylene glycol); or any combinationthereof.

The solvent serves to adjust a viscosity of the heating element formingcomposition so that a resistance heating element may be manufactured bya spraying method. An amount of the solvent is not particularly limitedand may be up to several hundred times a weight of the matrix particles.For example, the amount of the solvent may be in a range of about 5 toabout 50,000 parts by weight, particularly, about 10 to about 2,000parts by weight, about 20 to about 1,000 parts by weight, or about 25 toabout 900 parts by weight based on 100 parts by weight of the matrixparticles. The amount of the solvent may be increased or decreased toadjust the viscosity of the heating element forming composition.

The heating element forming composition may further include an additive,for example, at least one of a dispersion stabilizer, an oxidationstabilizer, a weather stabilizer, an antistatic agent, a dye, a pigment,and a coupling agent. The amount of the additive in the heating elementforming composition is within a range which does not deteriorate theheat generating effects of the heating element.

Among these additives, the dispersion stabilizer improves the dispersionstability of the conductive inorganic filler and provides orientation tothe filler so as to prevent aggregation of the conductive inorganicfiller and improve dispersibility. Thus, percolation characteristics ofthe conductive inorganic filler may be improved and electricalconductivity and heat generating characteristics of the prepared heatingelement may be improved. Examples of the dispersion stabilizer mayinclude a low molecular weight amine compound, an amine oligomer, anamine polymer, or any combination thereof.

When the surface of a nano-sheet type conductive inorganic filler iscapped by the dispersion stabilizer, aggregation may be prevented anddispersibility may be improved.

The heating element forming composition may further include a binder.The binder may improve coating properties, heat generatingcharacteristics, and properties of a film including the heating elementby improving dispersibility of the conductive inorganic filler and theviscosity of the heating element forming composition.

For example, the binder may include at least one of a cellulose polymer,a (meth)acrylic acid polymer, a styrene polymer, a polyvinyl resin, a(meth)acrylic acid (C1-C6 alkyl) ester polymer, a styrene-(meth)acrylicacid (C1-C6 alkyl) ester copolymer, a polyvinyl butyral, a polyvinylalcohol, a polyethylene oxide, a polypropylene carbonate, a polymethyl(meth)acrylate, an ammonium (meth)acrylate, an Arabic gum, a gelatin, analkyd resin, a butyral resin, a saturated polyester, a unsaturatedpolyester resin, a natural rubber, a silicone rubber, a fluorosilicone,a fluoroelastomer, a synthetic rubber, or a copolymer thereof. Forexample, the cellulose polymer may be used as the binder to improvecoating properties and heat generating characteristics of the heatingelement.

The heating element forming composition solution is prepared bydissolving the surface-functionalized matrix particles and theconductive inorganic filler, and if desired, the additive such as thedispersion stabilizer, in the solvent. Then the binder may be added tothe composition solution.

The heating element forming composition may have a viscosity suitable tobe sprayed without causing clogging of a nozzle, but the specificviscosity is not particularly limited. For example, a viscosity of about10 to about 30 seconds in a Ford Cup #4 (e.g., about 20 to about 100centipoise) is suitable for general spraying. However, when a specialspray gun is used, an amount of the solvent may be increased ordecreased to suitably adjust the viscosity.

The heating element forming composition may include about 5 to about99.99% by volume of the surface-functionalized matrix particles andabout 0.01 to about 95% by volume of the conductive inorganic fillerbased on a total volume of the surface-functionalized matrix particlesand the conductive inorganic filler. For example, the heating elementforming composition may include about 70 to about 99.99% by volume ofthe surface-functionalized matrix particles and about 0.01 to about 30%by volume of the conductive inorganic filler, or about 80 to about99.99% by volume of the surface-functionalized matrix particles andabout 0.01 to about 20% by volume of the conductive inorganic filler,based on the total volume of the surface-functionalized matrix particlesand the conductive inorganic filler. Within these ranges, the conductiveinorganic filler forms a conductive network at interfaces between thematrix particles, and thus a heating element may have electricalconductivity.

The heating element forming composition may include about 5 to about 500parts by volume of the dispersion stabilizer, for example about 10 toabout 300 parts by volume, particularly for example about 50 to about200 parts by volume, based on 100 parts by volume of the total volume ofthe surface-functionalized matrix particles and the conductive inorganicfiller. Within these ranges, the heating element forming composition mayhave uniform dispersibility and excellent coating properties.

FIGS. 1A to 1E are scanning electron microscope (SEM) images of aheating element manufactured using surface-functionalized matrixparticles and RuO₂ nano-sheets according to an embodiment. FIG. 1B showsthe distribution of the RuO₂ nano-sheets, FIG. 1C shows the distributionof Ru atoms, FIG. 1D shows the distribution of Si atoms, and FIG. 1Dshows the distribution of O atoms in the heating element. FIGS. 1F to 11are SEM images of a heating element manufactured usingsurface-unfunctionalized matrix particles and RuO₂ nano-sheets. FIG. 1Fis a cross section of the heating elements, FIG. 1G shows thedistribution of Ru atoms, FIG. 1H shows distribution of Al atoms, andFIG. 11 shows the distribution of O atoms.

As illustrated in FIGS. 1A to 1E, it is confirmed that RuO₂ nano-sheetsform a conductive network along interfaces between the matrix particlesin the heating element according to an embodiment. On the contrary, RuO₂nano-sheets do not form a conductive network although the RuO₂nano-sheets are uniformly distributed over the entire structure in theheating element shown in FIGS. 1F to 11.

Hereinafter, a method of manufacturing a heating element will bedescribed.

FIG. 2 is a schematic diagram for describing a method of manufacturing aheating element according to an embodiment.

First, a composition for forming a heating element is prepared.

The method may include functionalizing surfaces of the matrix particleswith positive charges or negative charges and combining thesurface-functionalized matrix particles 6, the conductive inorganicfiller 8, and a solvent. The method may further include adding adispersion stabilizer 2 to stabilize the conductive inorganic filler 8to prevent aggregation thereof and/or selectively adding a binder 4 tothe solution obtained thereby. The aforementioned steps may beconsidered preprocessing procedures for preparing the heating elementforming composition.

The preprocessing procedures may be performed to uniformly disperse eachof the raw materials in the solvent. The raw materials used to preparethe heating element forming composition are as described above.

The prepared heating element forming composition is coated on asubstrate.

The method of coating the heating element forming composition mayinclude screen printing, ink jet printing, dip coating, spin coating, orspray coating.

For example, the heating element forming composition may be coated onthe substrate by spray coating. In this case, the heating elementforming composition may be spray-coated at a rate of about 10 to about500 milliliters per minute (mL/min). In addition, a distance between theheating element forming composition and the substrate may be in a rangeof about 0.1 meter (m) to about 1 m, particularly, about 0.2 m to about0.9 m, and more particularly, about 0.3 m to about 0.8 m.

When coating the heating element forming composition, an amount of theheating element forming composition which is sprayed may be adjusted andthe coating procedure may be repeated several times such that a finallyobtained heating element, after evaporation of the solvent by heattreatment, has a predetermined thickness.

Next, the substrate coated with the heating element forming compositionis heat-treated to evaporate the solvent included in the heating elementforming composition, and the coating is cured to obtain the heatingelement. The heat treatment may be performed at a temperature in a rangeof about 300° C. to about 1,200° C., or about 500 to about 1,100° C., orabout 750° C. to about 1,000° C.

For example, the coated substrate is dried at a temperature of about100° C. to about 200° C. to evaporate the solvent. The coated substratefrom which the solvent is removed is heat-treated at a temperature ofabout 500° C. to about 900° C. for about 1 to about 20 minutes. Thetemperature for heat treatment of the substrate may vary depending upona material used to form the substrate, a type of the matrix particles, athickness of the coated composition, and the like.

The heat treatment may be performed by using, for example, a hot plate,without being limited thereto.

It may be confirmed that the heating element prepared as described abovehas a conductive network of the conductive inorganic filler formed atinterfaces between the matrix particles, as shown in FIG. 1.

The heating element may be formed in a single layer.

The heating element may be a sheet type heating element formed on thesubstrate.

FIG. 3 is a schematic cross-sectional view of a sheet type heatingelement using a heating element according to an embodiment.

Referring to FIG. 3, a heating element 40 is formed on a substrate 30.The substrate 30 may be a single layer or include multiple layers. Theheating element 40 may be formed on the substrate 30 through a series ofprocesses, for example, a coating process and a drying process. Theheating element 40 may generate heat by energy supplied by an externalsource. The energy may be electrical energy, but any energy that may beapplied to the heating element 40 to facilitate heat generation may alsobe used, without limitation. The entire structure of the substrate 30and the heating element 40 may be referred to as a heating elementstructure.

An upper layer 50 may further be disposed on the heating element 40. Theupper layer 50 may be a single layer or include multiple layers. Theentire structure of the substrate 30, the heating element 40, and theupper layer 50 may also be referred to as a heating element structure.

A composition of the substrate 30 may be the same as or different fromthe composition of the matrix particles. For example, the substrate 30may include at least one of a silicon oxide, a lithium oxide, a nickeloxide, a cobalt oxide, a boron oxide, a potassium oxide, an aluminumoxide, a titanium oxide, a manganese oxide, a copper oxide, a zirconiumoxide, a phosphorus oxide, a zinc oxide, a bismuth oxide, a lead oxide,or a sodium oxide. An amount of the oxide used to form the substrate 30may be the same as or different from the amount of oxide used to formthe matrix particles.

As another example, the substrate 30 may be formed of a materialdifferent from the material used to form the matrix particles. Forexample, the substrate 30 may be a silicon wafer, a metal substrate, oranother conductive substrate.

When the substrate 30 is a conductive substrate, a first insulatinglayer 24 may further be disposed between the substrate 30 and theheating element 40 as shown in FIG. 4. Also, a second insulating layer20 may further be disposed on a lower surface of the substrate 30. Thefirst and second insulating layers 20 and 24 may be the same ordifferent, and may be an oxide glass layer. The oxide glass layer mayinclude at least one of a silicon oxide, a lithium oxide, a nickeloxide, a cobalt oxide, a boron oxide, a potassium oxide, an aluminumoxide, a titanium oxide, a manganese oxide, a copper oxide, a zirconiumoxide, a phosphorus oxide, a zinc oxide, a bismuth oxide, a lead oxide,or a sodium oxide. The oxide glass layer may further include an enamellayer.

In FIG. 4, first and second electrodes 40A and 40B, respectively, areattached to opposite ends of the heating element 40. Electricity may besupplied to the heating element 40 from an external power source throughthe first and second electrodes 40A and 40B. The entire structure shownin FIG. 4 may also be referred to as a heating element structure.

Hereinafter, an apparatus including the heating element described abovewill be described with reference to the drawings.

Since the heating element described above may be used as a heat sourceemitting heat, the heating element may be used in an apparatus whichutilizes a heat source, and may be used as a heat generating componentor an electronic component. For example, the heating element describedabove may be applied to a printer, for example, a fuse of the printer.In addition, the heating element described above may also be applied toa thin film resistor or a thick film resistor.

FIG. 5 is a view of an apparatus including a heating element accordingto an embodiment as a heat source.

Referring to FIG. 5, an apparatus 80 includes a main body 82 and a firstheating element 84 included in the main body 82. The apparatus 80 may bean electrical apparatus or an electronic apparatus. For example, theapparatus 80 may be an oven. The main body 82 of the apparatus 80 mayhave an inner space 92 for accommodating an object. When the apparatus80 operates, energy (e.g., heat) may be supplied to the inner space 92to heat the object placed in the inner space 92 or to increase atemperature of the inner space 92. The first heating element 84 includedin the main body 82 of the apparatus 80 may be a heat source to supplythe energy to the inner space 92. The first heating element 84 may bearranged such that heat generated by the first heating element 84 isdistributed toward the inner space 92.

A second heating element 86 may further be provided in the main body 82.The second heating element 86 may be disposed to face the first heatingelement 84. The second heating element 86 may be arranged such that heatgenerated by the second heating element 86 is distributed toward theinner space 92. The first and second heating elements 84 and 86 may beheating elements formed of the same material or different materials. Inaddition, as marked as dashed lines, a third heating element 88 and afourth heating element 90 may further be provided in the main body 82.Alternatively, only one of the third heating element 88 and the fourthheating element 90 may be provided therein.

According to another embodiment, the main body 82 may include only thethird and fourth heating elements 88 and 90. An adiabatic member or athermal reflection member may be disposed between external boundarysurfaces of the main body 82 and each of the first through fourthheating elements 84, 86, 88, and 90.

FIG. 6 is a magnified cross-sectional view of a first region 80A of FIG.5.

Referring to FIG. 6, in the main body 82, an adiabatic material 82D anda case 82E are sequentially disposed in an upward direction from thethird heating element 88, and are between the third heating element 88and an external region. The case 82E may be an external case. Theadiabatic material 82D disposed between the case 82E and the thirdheating element 88 may extend to regions of the first, second, andfourth heating elements 84, 86, and 90 disposed in the main body 82. Theadiabatic material 82D is provided to prevent heat generated by thethird heating element 88 from being discharged to an outside of theapparatus 80.

A second insulating layer 82C, a substrate 82B, and a first insulatinglayer 82A are sequentially disposed in a downward direction from thethird heating element 88 between the third heating element 88 and theinner space 92. The first insulating layer 82A, the substrate 82B, thesecond insulating layer 82C, and the third heating element 88 aresequentially stacked from the inner space 92 towards the outside of theapparatus 80. The layered configuration may also be applied to theregions where the first, second, and fourth heating element 84, 86, and90 are arranged.

The first and second insulating layers 82A and 82C may be formed of thesame insulating material or different insulating materials. At least oneof the first and second insulating layers 82A and 82C may be an enamellayer, without being limited thereto, and thicknesses of the first andsecond insulating layers 82A and 82C may be the same or different. Thesubstrate 82B may be a support member that maintains a structure of themain body 82 of the apparatus 80 while supporting the first throughfourth heating elements 84, 86, 88, and 90. The substrate 82B may be,for example, a metal plate, but the present embodiment is not limitedthereto.

The stack structure including the heating element 88 as illustrated inFIG. 6 may also be applied to any other apparatuses (e.g., an electrichot pot) to heat an object (e.g., water) as well as the apparatusillustrated in FIG. 5. When the heating element 88 is disposed at thebottom of the apparatus and the object is disposed on the heatingelement 88, the adiabatic material 82D may be disposed under the heatingelement 88.

FIGS. 7A and 7B are cross-sectional views of another apparatus includingthe heating element described above. The apparatus of FIG. 7 may be aheating apparatus.

Referring to FIG. 7A, a first apparatus 102 is disposed inside a wall100. The first apparatus 102 may be a heating generation apparatusconfigured to emit heat toward the outside of a first surface of thewall 100. If the wall 100 is at least one of the walls that define aroom, the first apparatus 102 may be a heat generation apparatus thatemits heat to increase a temperature of the room or to warm up. Asillustrated in FIG. 7B, the first apparatus 102 may also be disposed ona surface of the wall 100.

Although not shown, the first apparatus 102 may also be installed apartfrom the wall 100. When the first apparatus 102 is arranged apart fromthe wall 100, the first apparatus 102 may be freely moved. Thus, a usedmay move the first apparatus 102 to an area desired by the user.

The first apparatus 102 may include a heating element (not shown) forgenerating heat therein. The first apparatus 102 may be buried in thewall 100. However, a panel for operating the first apparatus 102 may bedisposed on a surface of the wall 100. A second apparatus 104 mayfurther be disposed inside the wall 100. The second apparatus 104 may bea heat generation apparatus configured to emit heat toward the outsideof a second surface of the wall 100. If the wall 100 is at least one ofthe walls that define the room, the second apparatus 104 may be anapparatus that emits heat to warm up an adjacent room or another regionneighboring the room with the wall 100 therebetween. As illustrated inFIG. 7B, the second apparatus 104 may also be installed on a surface ofthe wall 100. Although not shown, the second apparatus 104 may also befreely moved apart from the wall 100 like the first apparatus 102. Thesecond surface may be a surface opposite to the first surface or facingthe first surface. The second apparatus 104 may include a heatingelement (not shown) that generates heat. The heating element may be aheat source for increasing a temperature of the outside of the secondsurface of the wall 100. Although most parts of the second apparatus 104may be buried inside the wall 100, a panel for operating the secondapparatus 104 may be disposed on a surface of the wall 100. In FIG. 7,arrows indicate heats emitted from the first and second apparatuses 102and 104.

Meanwhile, the first and second apparatuses 102 and 104 may haveattachable/detachable structures respectively. In this case, the firstapparatus 102 or the second apparatus 104 may be mounted on an innerside of a window. For example, assuming that reference numeral 100 ofFIG. 7B indicates not a wall but a window, the first apparatus 102 maybe a heating apparatus mounted on an inner side of the window 100. Inthis case, the second apparatus 104 may not be needed. When the firstapparatus 102 is mounted on the window, the first apparatus 102 may bemounted on a whole inner surface of the window or may be mounted on onlya part of the inner surface of the window.

According to another embodiment, the heating element described above maybe applied to a device or an apparatus that provides heat to a user. Forexample, the heating element described above may be applied to a hotpack or clothes (e.g., a jacket or a vest, gloves, or shoes) that may beworn by the user. In this case, the heating element may be provided onan inner side or inside a cloth.

According to another embodiment, the heating element described above maybe applied to a wearable device. The heating element described above mayalso be applied to outdoor equipment, for example, an apparatus thatemits heat in a cold atmosphere.

Hereinafter, one or more embodiments will be described in detail withreference to the following examples. However, these examples are notintended to limit the purpose and scope of the one or more embodiments.

EXAMPLES Experimental Example 1: Manufacture of Surface-FunctionalizedMatrix Particles and Evaluation of Dispersion Stability

In order to prepare a matrix surface-functionalized with negativecharges, 300 g of an enamel frit (D₅₀<100 μm, Hae Kwang EnamelIndustrial Co., Ltd.) was immersed in 1.2 L of a mixed solution ofammonia, water, and hydrogen peroxide (RCA solution) andsurface-treated. Thus, an enamel frit surface-treated with OH⁻ anionswas prepared.

Meanwhile, in order to prepare a matrix surface-functionalized withpositive charges, 100 g of an enamel frit (D₅₀<100 μm, Hae Kwang EnamelIndustrial Co., Ltd.) was surface-treated with a solution of(3-aminopropyl) triethoxysilane (APTES). Thus, an enamel fritsurface-treated with NH³⁺ cations was prepared.

Zeta potential, electric mobility, and surface charge distribution of anuntreated enamel frit, an enamel frits surface-treated with negativecharges, an enamel frit surface-treated with positive charges, and RuO₂nano-sheets (to be mixed therewith later) were measured and shown inFIGS. 8A and 8B.

In addition, in order to evaluate dispersion stability of the enamelfrits before and after surface treatment, 0.1 g of each of the neutralenamel frit which is surface-untreated, the enamel frits which aresurface-treated with positive charges, and the enamel frits which aresurface-treated with negative charges, was dispersed in water andsubjected to a sedimentation test. Test results thereof after 1 day(about 24 hours) are shown in FIG. 9.

To evaluate dispersion stability of mixed slurries of the enamel fritsand the RuO₂ nano-sheets before and after surface treatment, 0.2 g ofRuO₂ nano-sheets and 1.8 g of each of the neutral surface-untreatedenamel frit, the enamel frits surface-treated with positive charges, andthe enamel frits which are surface-treated with negative charges weredispersed in water to prepare slurries and the slurries were subjectedto a sedimentation test. Test results thereof after 1 day are shown inFIG. 10.

Referring to FIGS. 9 and 10, it was confirmed that the mixed slurry ofthe enamel frit surface-treated with negative charges and the RuO₂nano-sheets (having negative surface charges) had excellent dispersionstability. On the contrary, when the enamel frit surface-treated withpositive charges is mixed with the RuO₂ nano-sheets (having oppositesurface charges thereto), aggregation occurs and thus dispersionstability may deteriorate. In the case of using the neutral enamel fritwhose surface was not treated, the degree of aggregation is lower thanin the case of the positively charged enamel frit, but greater than inthe case of the negative charged enamel frit.

Surface potential, charge mobility, and dispersibility of each of thematerials and mixed solutions thereof was measured in the case wherehydroxypropyl methylcellulose (HPMC) was added to the composition as acellulose-based binder, and the results are shown in Table 4 below.

Here, f-enamel is an enamel frit surface-functionalized with anions(i.e., having negative charges) and amounts of the materials included inthe mixed solutions are shown in Table 5 below. In addition,dispersibility is a value obtained by measuring transmittance of lightwith respect to a height of a sample over time using light scatteringwith a Turbiscan equipment.

TABLE 4 Surface Charge potential mobility Dispersibility Material (mV)(cm²/V) (%) Component HPMC 0 1.26E−03 100 RuO₂ NS −57.4 1.62E−04 100Enamel −35.5  2.9E−04 30 f-enamel −39.6  3.1E−04 50 Mixed RuO₂ NS-HPMC−57.4 1.62E−04 100 solution f-enamel-HPMC −113.6 3.20E−04 80 RuO₂NS/Enamel N/A N/A 40 RuO₂ NS/f-Enamel N/A N/A 70 RuO₂/f-enamel-HPMC N/AN/A 99

TABLE 5 Mixed solution RuO₂ Enamel HPMC RuO₂ NS-HPMC 0.2 g (50 mL)   0 g0.5 g f-enamel-HPMC 0.2 g (50 mL) 1.8 g 0.5 g RuO₂ NS/Enamel 0.2 g (50mL) 1.8 g   0 g RuO₂ NS/f-Enamel 0.2 g (50 mL) 1.8 g   0 gRuO₂/f-enamel-HPMC 0.2 g (50 mL) 1.8 g 0.5 g

As shown in Table 4, while the surface-untreated enamel frit alone had adispersibility of only 30%, the dispersibility was increased to 50%after surface-functionalization with anions. After surface treatment, itwas confirmed that the dispersibility of the enamel frit was improvedeven after being mixed with the RuO₂ nano-sheets. In addition, thedispersibility was increased to 99% when the enamel frit surface-treatedwith anions was mixed with the RuO₂ nano-sheets and the cellulose-basedbinder.

Experimental Example 2: Evaluation of Performance of Heating ElementUsing Surface-Functionalized Matrix Particles

1.8 g of the enamel frit surface-treated with negative charges andprepared according to Experimental Example 1 and 0.2 g of the RuO₂nano-sheets capped with the TBAOH described above were dispersed in 50mL of water to prepare a coating solution. The coating solution wasspray-coated on an enamel substrate at room temperature and dried at atemperature of about 110 to about 120° C. for 10 minutes. Then, thecoated resultant was heat-treated at 750° C. for 16 minutes tomanufacture a heating element.

Electrical conductivity with respect to mixing ratios of RuO₂nano-sheets was measured and the results are shown in FIG. 11.Electrical conductivity was measured as follows. A silver (Ag) paste wasapplied to opposite ends of the manufactured heating element and driedto form electrodes. Electrical conductivity of the heating element wasmeasured by measuring resistance between the electrodes and measuring awidth, a length, and a thickness of the heating element.

As illustrated in FIG. 11, it may be confirmed that the heating elementprepared using the surface-treated enamel frit has better electricalconductivity than the heating element prepared using thesurface-untreated enamel frit.

In addition, FIG. 12 illustrates thickness and electrical conductivityof heating elements in which 1 volume percent (vol %) of the RuO₂nano-sheets is combined with either the surface-functionalized enamelfrit (f-enamel) or the surface-unfunctionalized enamel frit (enamel). Asillustrated in FIG. 12, even when the enamel frits were mixed with thesame amount of the RuO₂ nano-sheets, the heating element manufacturedusing the surface-treated enamel frit had a far greater electricalconductivity despite having a smaller thickness.

Meanwhile, the quality of a film formed of the heating elementmanufactured using the surface-treated enamel frit and 1% by volume ofthe RuO₂ nano-sheets was measured and is shown in FIG. 13. A surfaceroughness of the heating element was 2.14 μm at a film thickness of 22μm indicating uniform surface characteristics.

FIGS. 14A to 14D illustrate the film morphology of the heating elementshaving various thicknesses, in the case where the surface-untreated orsurface-treated enamel frits and the RuO₂ nano-sheets (1 vol) were used.As shown in FIGS. 14A to 14D, it may be confirmed that the heatingelement manufactured using the surface-treated enamel frit (FIG. 14D)forms a clean and clear film at a small thickness of 20 μm indicating astable coating force even after sintering.

Experimental Example 3: Evaluation of Capping Effect of RuO₂ Nano-SheetsUsing Dispersion Stabilizer

In order to confirm the capping effect of the RuO₂ nano-sheets in thecase where the enamel frit is surface-treated with negative charges andprepared according to Experimental Example 1 above and a dispersionstabilizer is used, the following procedure was performed.

The surfaces of the RuO₂ nano-sheets were stabilized usingtetrabutylammonium hydroxide (TBAOH) as the dispersion stabilizer, thestabilization occurring via intermolecular forces such as van der Waalsforces or hydrogen bonds. 1.8 g of the enamel frit surface-treated withnegative charges and prepared according to Experimental Example 1described above and 0.2 g of the RuO₂ nano-sheets capped with TBAOH weredispersed in 50 mL of water to prepare a coating solution. The coatingsolution was spray-coated on an enamel substrate at room temperature andthe coated resultant was dried at a temperature of about 110° C. toabout 120° C. for 10 minutes and heat-treated at 750° C. for 16 minutes,thereby completing the manufacture of a heating element.

The performance of coating solutions and heating elements including theenamel frit surface-treated with negative charges and prepared accordingto Experimental Example 1 and RuO₂ nano-sheets before and after beingcapped with TBAOH, are shown in FIGS. 15A and 15B, and in Table 6 below.

FIGS. 15A and 15B are photographs showing the dispersion stability ofcoating solutions in the presence (FIG. 15B) and absence (FIG. 15A) ofTBAOH.

Table 6 below shows the viscosity and dispersibility of the coatingsolutions and the thickness variation and electrical conductivity offilms including the heating elements in the presence and absence ofTBAOH.

TABLE 6 No TBAOH With TBAOH Viscosity (cps) 354 303 Dispersibility (%)40 99 Thickness variation (%) 35 9.6 Electrical conductivity (S/m) 0.01165

As shown in FIG. 15 and Table 6, it may be confirmed that when the RuO₂nano-sheets capped with the dispersion stabilizer are used,dispersibility of the coating solution is further improved andelectrical conductivity of the heating element is further increased.

In addition, in order to compare film quality and electricalconductivity of a heating element according to the amount of TBAOH,heating elements were manufactured using RuO₂ nano-sheets capped with0.1% by weight, 0.5% by weight, 1% by weight, and 2% by weight of TBAOH.FIGS. 16A to 16E are photographs showing the film quality of the heatingelements. FIG. 17 is a graph illustrating electrical conductivity andsurface roughness of the heating elements with varying TBAOH content.

As shown in FIGS. 16 and 17, it may be confirmed that both the filmquality and electrical conductivity of the heating element were improvedin the case where the RuO₂ nano-sheets were stabilized by using 2% byweight or less of the dispersion stabilizer, as compared to the case ofnot using the dispersion stabilizer. In particular, when about 1% byweight of the dispersion stabilizer was used, the heating elementexhibited the best film quality and the highest electrical conductivity.However, when the amount of the dispersion stabilizer is greater thanabout 2% by weight, the film quality and electrical conductivity of theheating element deteriorated. Without being limited by theory, it isbelieved that this occurred because excessive capping of the conductiveinorganic filler may deteriorate formation of the conductive network.

Experimental Example 4: Evaluation of Effect of Binder

In order to identify the effects of using the enamel fritsurface-treated with negative charges and prepared according toExperimental Example 1 and a binder, experiments were performed asfollows.

0.5 g of hydroxypropyl methylcellulose (HPMC) was added to a coatingsolution prepared by dispersing 1.8 g of the enamel frit surface-treatedwith negative charges and prepared according to Experimental Example 1and 0.2 g of RuO₂ nano-sheets in 50 mL of water. The coating solutionwas spray-coated onto an enamel substrate at room temperature and thecoated substrate was dried at a temperature of about 110° C. to about120° C. for 10 minutes and heat-treated at 750° C. for 16 minutes tomanufacture a heating element.

Table 7 below shows viscosity, dispersibility of coating solutions andthickness variations and electrical conductivity of the heating elementsmanufactured using the same in the presence and absence of HPMC.

TABLE 7 No HPMC with HPMC Viscosity (cps) 4 354 Dispersibility (%) 40 80Thickness variation (%) 35 15 Electrical conductivity (S/m) 0.47 19.35

As shown in Table 7, the viscosity of the coating solution variesaccording to the type of polymer binder. Since the organic stabilizer isan oligomer, it may be seen that viscosity is not considerablyinfluenced thereby.

FIGS. 18A and 18B are photographs showing dispersion stability of thecoating solutions and the quality of films including the heatingelements in the presence (FIG. 18B) and absence of HPMC (FIG. 18A). Asshown in FIGS. 18A and 18B, it may be seen that as the amount of thebinder increases, the dispersion stability of the coating solution andthe quality of the film of the heating element are further improved.

Experimental Example 5: Comparison and Evaluation of Thermal Propertiesof Sheet Type Heating Element (1) Preparation of Coating Solution

In order to compare and evaluate thermal properties of sheet typeheating elements according to the composition of the coating solution,coating solutions are prepared as shown in Table 8 below.

TABLE 8 Composition Matrix Filler Stabilizer Binder (1) No treatmentEnamel RuO₂ NS TBAOH HPMC (1.8 g) (0.2 g/50 mL)   (0 g)   (0 g) (2)w/HPMC Enamel RuO₂ NS TBAOH HPMC (1.8g) (0.2 g/50 mL)   (0 g) (0.5 g)(3) w/HPMC-TBAOH Enamel RuO₂ NS TBAOH HPMC (1.8 g) (0.2 g/50 mL) (0.5 g)(0.5 g) (4) f-enamel w/ F-enamel RuO₂ NS TBAOH HPMC HPMC-TBAOH (1.8 g)(0.2 g/50 mL) (0.5 g) (0.5 g)

(2) Method of Preparing Coating Solution

An amine-based stabilizer (TBAOH) is mixed with a colloidal solution ofRuO₂ NS used as a conductive filler and a binder (HPMC) is addedthereto. The mixture is stirred for about 1 day (about 24 hours). Incase of further adding polyethyleneimine (PE) thereto as the amine-basedstabilizer, a mixture of TBAOH and PEI is stirred for about 1 day (about24 hours) and then the binder (HPMC) is further added thereto andstirred. After stirring, the solution in which the RuO₂ NS, thestabilizer, and the binder are uniformly mixed and asurface-functionalized enamel frit are mixed to prepare a slurry coatingsolution.

(3) Method for Evaluating Heat Generating Characteristics

Temperatures of heating elements coated on a fabricated plate aremonitored in real time while increasing a voltage by supplying a currentto the heating elements. The temperatures of the heating elements areindirectly measured by using a thermal imager or a non-contacttemperature meter. The heat generating characteristics are obtained bymeasuring whether or not the temperature continuously increases or isinterrupted due to a short circuit as the applied voltage continuouslyincreases. A highest temperature of the heating element without cracksor fails in accordance with application of the voltage is determined asa highest heating temperature.

(4) Evaluation Results

FIG. 19 is a graph illustrating evaluation results of thermal propertiesof the heating elements. FIG. 20 visually illustrates the thermalproperties of the heating elements of FIG. 19 respectively. In FIGS. 19and 20, 33 V and 152 V indicate withstand voltages at each temperature.As the withstand voltage increases, power increases and voltagebreakdown of a heat generating conductor decreases, thereby improvingheat generating characteristics.

As shown in FIGS. 19 and 20, in the case of using thesurface-functionalized enamel frit, excellent heat generatingcharacteristics may be accomplished with a small amount of RuO₂nano-sheets. Similar heat generating characteristics may be obtainedwith about a quarter amount of RuO₂ nano-sheets in comparison with thecase of using the surface-unfunctionalized enamel frit.

The heating element forming composition according to an embodiment maymanufacture a heating element having excellent dispersion stability,high quality of the film even with a small amount of the conductiveinorganic filler, high electrical conductivity, and excellent heatgenerating characteristics.

It should be understood that embodiments described herein should beconsidered in a descriptive sense only and not for purposes oflimitation. Descriptions of features or aspects within each embodimentshould be considered as available for other similar features or aspectsin other embodiments.

While one or more embodiments have been described with reference to thefigures, it will be understood by those of ordinary skill in the artthat various changes in form and details may be made therein withoutdeparting from the spirit and scope as defined by the following claims.

What is claimed is:
 1. A heating element comprising: a plurality ofmatrix particles; and a conductive inorganic filler disposed atinterfaces between the plurality of matrix particles to provide aconductive network.
 2. The heating element of claim 1, wherein theheating element comprises about 5% to about 99.9% by volume of thematrix particles and about 0.01% to about 95% by volume of theconductive inorganic filler, based on a total volume of the matrixparticles and the conductive inorganic filler.
 3. The heating element ofclaim 1, wherein the heating element comprises about 95% to about 99.9%by volume of the matrix particles and about 0.1% to about 5% by volumeof the conductive inorganic filler, based on a total volume of thematrix particles and the conductive inorganic filler.
 4. The heatingelement of claim 1, wherein an effective conductivity of the heatingelement is 30% or greater, wherein effective conductivity is an amountof the conductive inorganic filler contributing actual electricalconductivity compared to the total amount of the conductive inorganicfiller.
 5. The heating element of claim 1, wherein the conductiveinorganic filler is in a form of nano-sheets, nano-rods, or anycombination thereof.
 6. The heating element of claim 1, wherein theconductive inorganic filler is in a form of nano-sheets having athickness of about 1 nanometer to about 1,000 nanometers.
 7. The heatingelement of claim 1, wherein the conductive inorganic filler comprises atleast one of an oxide, a boride, a carbide, or a chalcogenide.
 8. Theheating element of claim 7, wherein the oxide comprises RuO₂, MnO₂,ReO₂, VO₂, OsO₂, TaO₂, IrO₂, NbO₂, WO₂, GaO₂, MoO₂, InO₂, CrO₂, RhO₂, orany combination thereof, the boride comprises Ta₃B₄, Nb₃B₄, TaB, NbB,V₃B₄, VB, or any combination thereof, the carbide comprises Dy₂C, Ho₂C,or any combination thereof, and the chalcogenide comprises AuTe₂, PdTe₂,PtTe₂, YTe₃, CuTe₂, NiTe₂, IrTe₂, PrTe₃, NdTe₃, SmTe₃, GdTe₃, TbTe₃,DyTe₃, HoTe₃, ErTe₃, CeTe₃, LaTe₃, TiSe₂, TiTe₂, ZrTe₂, HfTe₂, TaSe₂,TaTe₂, TiS₂, NbS₂, TaS₂, Hf₃Te₂, VSe₂, VTe₂, NbTe₂, LaTe₂, CeTe₂, or anycombination thereof.
 9. The heating element of claim 1, wherein thematrix particles comprise a glass, an organic polymer, or anycombination thereof.
 10. The heating element of claim 9, wherein theglass is formed from a frit comprising at least of silicon oxide,lithium oxide, nickel oxide, cobalt oxide, boron oxide, potassium oxide,aluminum oxide, titanium oxide, manganese oxide, copper oxide, zirconiumoxide, phosphorus oxide, zinc oxide, bismuth oxide, lead oxide, orsodium oxide.
 11. The heating element of claim 9, wherein the glass isformed from a glass frit comprising at least one of a zinc oxide-siliconoxide, a zinc oxide-boron oxide-silicon oxide, a zinc oxide-boronoxide-silicon oxide-aluminum oxide, a bismuth oxide-silicon oxide, abismuth oxide-boron oxide-silicon oxide, a bismuth oxide-boronoxide-silicon oxide-aluminum oxide, a bismuth oxide-zinc oxide-boronoxide-silicon oxide, or a bismuth oxide-zinc oxide-boron oxide-siliconoxide-aluminum oxide compound.
 12. The heating element of claim 9,wherein the organic polymer comprises at least one of a polyimide, apolyphenylenesulfide, a polybutylene terephthalate, a polyamideimide, aliquid crystalline polymer, a polyethylene terephthalate, apolyphenylene sulfide, or a polyetheretherketone.
 13. A composition forforming a heating element, the composition comprising functionalizedmatrix particles, a conductive inorganic filler, and a solvent.
 14. Thecomposition of claim 13, wherein the matrix particles comprise a glass,an organic polymer, or any combination thereof.
 15. The composition ofclaim 14, wherein the glass is formed from a glass frit comprising atleast one of a silicon oxide, a lithium oxide, a nickel oxide, a cobaltoxide, a boron oxide, a potassium oxide, an aluminum oxide, a titaniumoxide, a manganese oxide, a copper oxide, a zirconium oxide, aphosphorus oxide, a zinc oxide, a bismuth oxide, a lead oxide, or asodium oxide.
 16. The composition of claim 14, wherein the glass isformed from a glass frit comprising at least one of a zinc oxide-siliconoxide, a zinc oxide-boron oxide-silicon oxide, a zinc oxide-boronoxide-silicon oxide-aluminum oxide, bismuth oxide-silicon oxide-, abismuth oxide-boron oxide-silicon oxide, a bismuth oxide-boronoxide-silicon oxide-aluminum oxide, a bismuth oxide-zinc oxide-boronoxide-silicon oxide, or a bismuth oxide-zinc oxide-boron oxide-siliconoxide-aluminum oxide compound.
 17. The composition of claim 14, whereinthe organic polymer comprises at least one of a polyimide, apolyphenylenesulfide, a polybutylene terephthalate, a polyamideimide, aliquid crystalline polymer, a polyethylene terephthalate (PET), apolyphenylene sulfide, or a polyetheretherketone.
 18. The composition ofclaim 13, wherein the matrix particles are surface-functionalized withpositive charges or negative charges.
 19. The composition of claim 13,wherein the matrix particles are surface-functionalized with negativecharges and comprise at least one of hydroxide ion (OH), a sulfate ion(SO₄ ²⁻), a nitrate ion (NO₃ ⁻), an acetate ion (CH₃COO⁻), apermanganate ion (MnO₄ ⁻), a carbonate ion (CO₃ ²⁻), a sulfide ion(S²⁻), a chloride ion (Cl⁻), a bromide ion (Br⁻), or an oxide ion (O²⁻).20. The composition of claim 13, wherein the conductive inorganic filleris in a form of nano-sheets, nano-rods, or any combination thereof. 21.The composition of claim 13, wherein the conductive inorganic filler isin a form of nano-sheets having a thickness of about 1 nanometer toabout 1,000 nanometers.
 22. The composition of claim 13, wherein theconductive inorganic filler has an electrical conductivity of 1,250Siemens per meter or greater.
 23. The composition of claim 13, whereinthe conductive inorganic filler comprises at least one of an oxide, aboride, a carbide, or a chalcogenide.
 24. The composition of claim 23,wherein the oxide comprises RuO₂, MnO₂, ReO₂, VO₂, OsO₂, TaO₂, IrO₂,NbO₂, WO₂, GaO₂, MoO₂, InO₂, CrO₂, RhO₂, or any combination thereof, theboride comprises Ta₃B₄, Nb₃B₄, TaB, NbB, V₃B₄, VB, or any combinationthereof, the carbide comprises Dy₂C, Ho₂C, or any combination thereof,and the chalcogenide comprises AuTe₂, PdTe₂, PtTe₂, YTe₃, CuTe₂, NiTe₂,IrTe₂, PrTe₃, NdTe₃, SmTe₃, GdTe₃, TbTe₃, DyTe₃, HoTe₃, ErTe₃, CeTe₃,LaTe₃, TiSe₂, TiTe₂, ZrTe₂, HfTe₂, TaSe₂, TaTe₂, TiS₂, NbS₂, TaS₂,Hf₃Te₂, VSe₂, VTe₂, NbTe₂, LaTe₂, CeTe₂, or any combination thereof. 25.The composition of claim 13, further comprising at least one of adispersion stabilizer, an oxidation stabilizer, a weather stabilizer, anantistatic agent, a dye, a pigment, or a coupling agent.
 26. Thecomposition of claim 25, wherein the dispersion stabilizer comprises alow-molecular-weight amine compound, an amine oligomer, an aminepolymer, or any combination thereof.
 27. The composition of claim 13,further comprising a binder, wherein the binder comprises at least oneof a cellulose polymer, a (meth)acrylic acid polymer, a styrene polymer,a polyvinyl resin, a (meth)acrylic (C1-C6 alkyl) ester polymer, astyrene-(meth)acrylic (C1-C6 alkyl) ester copolymer, a polyvinylbutyral, a polyvinyl alcohol, a polyethylene oxide, a polypropylenecarbonate, a polymethyl (meth)acrylate, an ammonium (meth)acrylate, anArabic gum, a gelatin, an alkyd resin, s butyral resin, s saturatedester polymer, a natural rubber, a silicone rubber, a fluorosilicone, afluoroelastomer, a synthetic rubber, or any copolymer thereof.
 28. Thecomposition of claim 13, wherein the composition comprises: about 5% toabout 99.9% by volume of the matrix particles and about 0.01% to about95% by volume of the conductive inorganic filler, based on a totalvolume of the matrix particles and the conductive inorganic filler, andabout 5 parts to about 500 parts by volume of the solvent based on 100parts by volume of the total volume of the functionalized matrixparticles and the conductive inorganic filler.
 29. A heating apparatuscomprising the heating element according to claim
 1. 30. A method ofmanufacturing a heating element, the method comprising: coating thecomposition for forming a heating element of claim 13 on a substrate;and heat-treating the coated substrate to provide the heating element.31. The method of claim 30, wherein the coating is performed by spraycoating.
 32. The method of claim 30, wherein the heat-treating isperformed at a temperature of about 300° C. to about 1200° C.
 33. Amethod of manufacturing a composition for forming a heating element, themethod comprising: functionalizing surfaces of matrix particles withpositive charges or negative charges; and combining thesurface-functionalized matrix particles, a conductive inorganic filler,and a solvent.
 34. The method of claim 33, wherein the functionalizingis performed by functionalizing the surfaces of the matrix particleswith positively or negatively charged functional groups.